PROJECT SUMMARY The overall goal of this competing renewal application remains focused on developing and leveraging quantitative molecular imaging biomarkers that take advantage of a synergy between PET and MR imaging to provide significantly improved guidance for cancer radiation therapy (RT) in sarcomas. Traditionally, definition of the radiotherapy target volume utilizes CT and (sometimes) MR images to delineate visible gross tumor volume (GTV) which is expanded by certain margins to account for microscopic disease according to clinical guidelines, forming the clinical target volume (CTV). The standard T1/T2 weighted MR images are unable to distinguish tumor infiltration from inflammation and therefore inclusion of edema into the CTV is left to the physician's judgment. For patients unable to have resection, definitive RT results in local control of only 40 to 75% with the failures occurring primarily within the gross tumor. Standard anatomic imaging does not allow identification of areas at risk of local failure. We hypothesize that multiparametric PET/MR imaging will help to identify potential areas of resistant cell populations within the tumor in order to prescribe the higher dose to these areas to increase treatment effectiveness.